Electric vehicles (EVs) are emerging as the preferred mode of transportation, offering a sustainable and environmentally friendly alternative to traditional combustion engine vehicles. Within the complex ecosystem of an EV, numerous electronic control units (ECUs) play crucial roles in ensuring their efficient operation. One such ECU is the motor control unit (MCU), which acts as the brain behind the motor's performance. In this comprehensive article, we will explore the world of motor control units, examining their functions, components, and the latest trends shaping the automotive MCU landscape.
Understanding the Motors Used in Electric Vehicles
Before delving into the intricacies of motor control units for electric vehicles, it is essential to understand the various types of motors commonly used in electric vehicles. The two most prevalent types are the Brushless DC (BLDC) motor and the Permanent Magnet Synchronous (PMS) motor.
The BLDC motor, also known as an electronically commutated motor, eliminates the need for brushes and commutators, resulting in improved efficiency and reduced maintenance. Essentially it has permanent magnets in the rotor and coil windings in the stator. By varying the electric current and its direction, the magnetic field produced by the stator drives the rotor with push/pull force. Both the speed and torque can be varied by changing the electric current through the coils. On the other hand, the PMS motor, also having permanent magnets in rotors, has coils wound in sinusoidal ways in the stator. Though the control mechanism is more complex, it offers higher power density ratio and overall performance.
BLDC and PMS motors dominate the market, with BLDC motors being favored in three-wheelers and PMS motors in two/four-wheelers. Additionally, a small percentage of electric vehicles in India employ induction motors.
Functions and Components of a Motor Control Unit (MCU)
The motor control unit serves as the central control hub for the electric vehicle's motor, performing several vital functions to ensure smooth and efficient driving. Its primary responsibility is to convert the direct current (DC) supplied by the battery into a three-phase alternating current (AC) that drives the motor.
Furthermore, the MCU monitors crucial parameters such as temperature, current, and voltage to optimize motor performance and prevent potential damage. It also controls the motor's speed, torque, and direction based on inputs from the driver or the vehicle's control system.
MCU architecture - Hardware perspective
This section details about the MCU architecture and a typical block diagram of a MCU is as follows:
The microcontroller at the center is responsible for executing complex control algorithms and managing the overall operation of the motor. It also provides an external digital interface, mostly a CAN, that allows it to communicate to other ECUs in the system and get control information from the VCU. Gate drivers facilitate the control of power switches and are driven by dedicated driver controller peripheral or PWM channels. The power electronics enable the conversion between DC and AC power. Typically, a six-MOSFET configuration is used to achieve this conversion and count increased to handle to current requirements of the motor. Various sensing circuits provide feedback on motor parameters such as its position, phase currents, temperature etc. for precise control.
Software Architecture of the automotive MCU
Like any embedded system, the software architecture of a motor control unit for electric vehicles follows a layered approach. The firmware consists of two major parts - motor control and communication. The motor control component monitors inputs from various sensors and drives the phase currents using complex mathematical functions. The communication part enables seamless control from external systems, allowing user interactions and customization of motor parameters such as speed and torque limits to suit different driving conditions and preferences.
It is crucial for the MCU architecture to conform to safety standards such as ISO26262. Additionally, it should be a highly reliable design that effectively manages power dissipation without compromising performance or user experience.
Driving Technologies in Motor Control Units
While multiple methods exist for driving motors, such as Trapezoidal control and Sinusoidal control, the Field Oriented Control (FOC) based drive has gained widespread adoption. Initially developed for AC motors, FOC optimizes the torque delivered by the motor by maximizing the quadrature component. When the magnetic fluxes from both the stator and rotor interact, a force is generated in the form of a vector with two components - d and q. The d component, perpendicular to the rotor axis, relates to the flux component, while the q component represents torque and is perpendicular to d. FOC allows for precise control of motor torque and speed by accurately determining the current position of the rotor and using complex mathematical equations to align the motor's magnetic field appropriately. Although this technique requires faster and higher processing power, FOC enhances motor efficiency, reduces energy losses, and improves overall system performance. By dynamically adjusting the motor's current and voltage, FOC-based drives achieve smoother acceleration, higher torque output, and better responsiveness.
Power Electronics in automotive MCU
Power electronics play a vital role in automotive MCUs, enabling the conversion and control of electrical power. Low voltage motors, typically below 100V, employ MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). In contrast, higher voltage motors utilize Gallium Nitride (GaN) power switches and Silicon Carbide (SiC)/Insulated Gate Bipolar Transistor (IGBT) drives.
GaN power switches offer advantages such as higher switching speeds, lower power losses, and improved thermal performance compared to traditional silicon-based switches. This results in more efficient motor control units with reduced energy consumption and increased power density.
On the other hand, SiC and IGBT drives provide higher operating temperatures and voltage capabilities, enhancing performance and reliability in demanding electric vehicle applications. These advanced power electronics technologies contribute to the optimization of automotive MCUs, enhancing the overall efficiency and performance of electric vehicles.
Enhancing Efficiency with Regenerative Braking
Regenerative braking is a significant feature in electric vehicles that allows the motor control unit for electric vehicles to harness and recover energy during deceleration and braking. Instead of dissipating kinetic energy as heat, regenerative braking converts it back into electrical energy, which is then stored in the vehicle's battery. This process requires sophisticated electronics and software mechanisms to effectively leverage the back electromotive force (EMF) generated.
By employing regenerative braking, motor control units can significantly enhance the efficiency and range of electric vehicles. This technology not only reduces energy wastage but also improves the overall driving experience by providing smoother and more controlled braking.
Multi-Motor EVs
The adoption of multi-motor electric vehicles is on the rise, driven by the desire for enhanced performance and efficiency. Multi-motor electric vehicles offer improved traction control, enhanced stability, and increased overall performance. These vehicles utilize multiple motors to drive individual wheels or subsystems, allowing for advanced torque vectoring and precise control of each wheel.
However, the implementation of multi-motor electric vehicles requires complex and costlier designs, as the motor control units associated with them must be capable of managing power distribution, torque allocation, and coordination between the motors. These control units utilize advanced algorithms and communication protocols to ensure seamless integration and synchronized operation.
Emerging Trends in Motor Control Units
The electric vehicle industry is constantly evolving, and motor control units continue to undergo significant advancements. One emerging trend is the development of motor control units capable of controlling multiple motors simultaneously. Additionally, there is a standardization of voltage levels, with more OEMs moving towards 48V. Once standardized, the industry may transition to higher voltages for improved efficiency. The shift towards zonal architecture is also expected to bring major changes to MCU architecture and its positioning. In terms of motors, two-wheeler OEMs are experimenting with motor placement, exploring both hub drive and mid-drive models. Significant improvements are being seen in the power electronics side with tight integration and better efficiency. Exciting evolutions are anticipated in this space soon.
Conclusion: Designing Motor control unit for electric vehicle
As electric vehicles gain popularity, the role of motor control units in revolutionizing their performance becomes increasingly critical. Automotive MCU's serve as the driving force behind the electric vehicle's motor, ensuring optimal performance and efficiency. With constant advancements in MCU architecture and technology, the future promises even more efficient, powerful, and sustainable electric vehicles. Embien, with its reliable team of engineers and rich partnership eco-system can deliver motor control units for electric vehicles in different power categories at attractive value propositions
